如何在流中使用 ES8 async/await?

问题描述

在 https://stackoverflow.com/a/18658613/779159 中是如何计算 md5 的示例使用内置加密库和流的文件.

In https://stackoverflow.com/a/18658613/779159 is an example of how to calculate the md5 of a file using the built-in crypto library and streams.

var fs = require('fs');
var crypto = require('crypto');

// the file you want to get the hash
var fd = fs.createReadStream('/some/file/name.txt');
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');

fd.on('end', function() {
    hash.end();
    console.log(hash.read()); // the desired sha1sum
});

// read all file and pipe it (write it) to the hash object
fd.pipe(hash);

但是是否可以将其转换为使用 ES8 async/await 而不是使用上面看到的回调，同时仍然保持使用流的效率?

But is it possible to convert this to using ES8 async/await instead of using the callback as seen above, but while still keeping the efficiency of using streams?

推荐答案

async/await 仅适用于承诺，不适用于流.有一些想法可以创建一个额外的类似流的数据类型，它会获得自己的语法，但这些都是高度实验性的，我不会详细介绍.

async/await only works with promises, not with streams. There are ideas to make an extra stream-like data type that would get its own syntax, but those are highly experimental if at all and I won't go into details.

无论如何，你的回调只是在等待流结束，这非常适合承诺.你只需要包装流:

Anyway, your callback is only waiting for the end of the stream, which is a perfect fit for a promise. You'd just have to wrap the stream:

var fd = fs.createReadStream('/some/file/name.txt');
var hash = crypto.createHash('sha1');
hash.setEncoding('hex');
// read all file and pipe it (write it) to the hash object
fd.pipe(hash);

var end = new Promise(function(resolve, reject) {
    hash.on('end', () => resolve(hash.read()));
    fd.on('error', reject); // or something like that. might need to close `hash`
});

现在你可以等待那个承诺:

Now you can await that promise:

(async function() {
    let sha1sum = await end;
    console.log(sha1sum);
}());

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